Direct microwave modulation and demodulation device

Abstract

A microwave circuit intended for either direct modulation or direct demodulation of a microwave link communications signal is characterized in that a local oscillator (8) is incorporated in the circuit. The local oscillator supplies two signals that are in phase opposition at 180 degrees. Each signal is sent to a phase shifter. The first phase shifter (9) supplies two signals that are in quadrature, at 0 and 90 degrees. The second phase shifter supplies two signals in quadrature at 180 and 270 degrees. The 0 and 180 degree signals are sent to a first mixer (2), while the 90 and 270 degree signals are sent to a second mixer (3). In the case of a modulator, the first and second mixers receive, respectively, in-phase and quadrature signals, and the outputs of the mixers are combined to form a modulated signal. In the case of a demodulator, a modulated signal is applied through a ÷2 divider to inputs of the two mixers, and in-phase and quadrature signals are obtained at respective mixer outputs.

What is claimed is: 
     
       1. A device for direct modulation or demodulation of microwaves, said device being comprised of first and second mixers that deliver (in demodulation) or receive (in modulation) respectively an in-phase signal and a quadrature signal, said first mixer being controlled by two signals whose phase angles are 0 and 180 degrees respectively, said second mixer being controlled by two signals whose phase angles are 90 and 270 degrees respectively, the four signals being delivered by first and second phase shifters, wherein said device further comprisies a voltage controlled local oscillator that supplies first and second signals in phase opposition, said first signal having a 0 degree phase angle and being supplied to said first phase shifter, and said second signal having a 180 degree phase opposition and being supplied to said second phase shifter. 
     
     
       2. A device as claimed in claim 1, wherein said first and second phase shifters each deliver two signals that are in quadrature, said two signals delivered by said first phase shifter, respectively having phase angles of 0 and 90 degrees, being supplied to said first said and second mixers respectively. 
     
     
       3. A device as claimed in claim 1, wherein said voltage controlled oscillator is comprised of first and second field effect oscillator transistors that are connected in parallel, and wherein: the sources are interconnected via a variable impedance comprised of two varactors controlled by two voltages; the gates are controlled by a circuit comprised of two microstrip lines coupled to a single dielectric resonator, the current flow in said microstrip lines being in mutually opposite directions; the drain currents are accordingly in phase opposition; said oscillator further comprising two additional amplifier transistors, one per output channel, whose gates are controlled by the drain currents of said first and second oscillator transistors. 
     
     
       4. A device as claimed in claim 1, wherein each of said two phase shifters is comprised of: a Wilkinson type structure comprised of localised elements, having an input receiving a signal from said oscillator, said structure dividing said oscillator signal into two signals sent respectively to:   a first in-phase channel comprising a variable phase shift circuit controlled by an unbiased transistor controlled by a regulating voltage, and a fixed phase shift circuit; and   a second channel in quadrature comprising a variable attenuator circuit controlled by two unbiased transistors, controlled by a regulating voltage, and a fixed phase shift circuit, said two regulating voltages serving to adjust the balance of the amplitudes and the 90 degree phase shift angle of said two channels.   
     
     
       5. A device as claimed in claim 1, wherein, in the case of said device being a demodulator, a modulated signal is applied to said first and second mixers through a ÷2 divider which is comprised of a field effect transistor having a single, bifurcated gate and two separate drains, the source thereof being grounded. 
     
     
       6. A device as claimed in claim 1, wherein, in the case of said device being a modulator, a Wilkinson type combiner is used which has first and second inputs receiving the outputs from said first and second mixers, and an output delivering a modulated signal.